While most rapid access and "instant" photographic products have been designed to provide a positive image, there has been interest in products which would provide a usable negative image. Thus, Type 55 P/N and Type 665 Polaroid Land films provide both a positive silver transfer image and a fully developed negative suitable for use as a negative in conventional printing techniques. In using these films, the positive and negative images are formed on separate supports, and the negative image is given a hardening and stabilizing treatment after separation from the positive image. U.S. Pat. No. 3,345,166 issued Oct. 3, 1967 to Edwin H. Land et al and U.S. Pat. No. 3,549,364 issued Dec. 22, 1970 to Meroe M. Morse disclose processes of this type.
U.S. Pat. No. 2,544,268 issued on Mar. 6, 1951 to Edwin H. Land discloses a process for forming a usable negative by dissolving unexposed silver halide and diffusing it into the layer of processing reagent which thereafter is separated from the developed silver halide emulsion layer.
U.S. Pat. No. 3,343,958 issued Sept. 26, 1967 to Meroe M. Morse discloses the use of a combination of cysteine and a nitrogenous base to form a complex of unexposed silver halide having sufficient stability that it would not be necessary to remove the complex from the developed negative image. U.S. Pat. No. 3,721,562 issued Mar. 20, 1973 to Edwin H. Land disclosed an integral system providing a usable negative, the unexposed silver halide being allowed to remain in the form of a stable complex, such as that disclosed in U.S. Pat. No. 3,343,958. The formation of pin holes in the resulting integral negative transparency was reduced by including a neutralizing layer in the spreader sheet.
U.S. Pat. No. 3,615,438 issued Oct. 26, 1971 to Edwin H. Land et al discloses the formation of negative images by solubilization and transfer of exposed silver halide.
U.S. Pat. No. 3,990,895 issued Nov. 9, 1976 to Edwin H. Land discloses the formation of an additive color negative image. The exposed silver halide was developed under conditions which give increased covering power. The unexposed silver halide could be removed by fixing, transferred to an image-receiving layer to provide a positive silver image, or retained in the developed negative.
U.S. Pat. 3,894,871 issued July 15, 1975 to Edwin H. Land discloses the formation of positive transparencies, both silver black and white and additive color, wherein the exposed silver halide is reduced to low covering power silver and the unexposed silver halide is converted to a high covering power silver in a layer containing silver precipitating nuclei.
U.S. Pat. No. 3,536,488 issued Oct. 27, 1970 to Edwin H. Land discloses the formation of positive additive color transparencies wherein the photosensitive silver halide emulsion layer contains silver precipitating nuclei and exposed silver halide is developed to low covering power silver and unexposed silver halide is converted to high covering power silver.